Pneumatic air brake systems are well known and in widespread use on freight and other trains. These air brake systems include a pneumatic reservoir, brake valve and brake cylinder on each individual rail car of the train. The brake valve on each car is connected to an air brake hose which is adapted to be interconnected to the air brake hoses of adjacent cars. In effect, a common air brake hose extends the length of the train. Pneumatic braking signals are transmitted to the brake valves of the rail cars from a locomotive through the air brake hose. The brakes of all the rail cars are therefore applied and released at generally the same time, although there is a propagation delay in the pneumatic control signal which causes the brakes of the cars closer to the locomotive to be applied and released sooner than the brakes of the cars toward the end of the train. The length of these braking time differentials are directly related to the length of the train.
Electronic Air Brake Systems (EABS), also sometimes known as electronically controlled pneumatic (ECP) brake systems, are also being incorporated into trains. Braking systems of this type include a car control unit (CCU) on each rail car. The CCUs are all powered by a supply provided by a power cable extending the length of the train. Control over the CCUs is also provided by signals transmitted over the cable from the locomotive. An advantage of EABS is that they are not susceptible to brake time differentials, since the electronic control enables all the brakes to be applied and released effectively simultaneously.
Rail cars also include handbrakes which allow the brakes of the car to be manually applied and released. Handbrakes of this type are known and in widespread use. They typically include a hand-operated actuator such as a wheel or lever which is mechanically linked to the brakes by a chain or other linkage. Through use of the actuator (e.g., by rotating the wheel) an operator causes the linkage to pull the brake pads into engagement with the wheels of the car. Since individual pneumatic brakes on some cars of a train are sometimes inoperable (e.g., if the air has leaked out of the pneumatic reservoir), the handbrakes are usually set whenever the rail car is parked in a yard. Before the rail car can be moved, the handbrake must be released. The release of the handbrakes requires an operator to physically board the car.
Before a train rolls out of a yard an operator typically travels the length of the train (generally on foot or riding a motorized vehicle) and inspects each rail car. During this inspection the operator will typically observe the status of the handbrakes by looking to see if the chain or other linkage exhibits the sufficient degree of slack that would be expected in a released handbrake. If it appears that the handbrake is not released, the operator must board the car and release the handbrake since the wheels can be damaged if they slide on the track (rather than rotate) when the train moves. The operator can also monitor and control other systems on the train during this procedure. For example, the open or closed state of hoppers, the temperature of refrigerators and load weights can be monitored and controlled. However, it can be inefficient and sometimes relatively unreliable to perform these actions in this manner.
It is evident that there is a continuing need for improved rail car monitor and control procedures. A system capable of positively monitoring and controlling systems on rail cars to a high degree of accuracy with a minimum of operator intervention would be particularly desirable. Any such system should be capable of being retrofit onto existing rail car brake and other systems without interfering with the operation of the existing systems. To be commercially viable it must also be capable of being efficiently manufactured and operated.